Internal combustion engines, and in particular those which use carburetors, have for many years used air filters to remove unwanted particulates from the combustion air stream before it enters the engine. Standard, stock air filters have been supplied in a multitude of dimensions by auto manufacturers, with each filter being adapted to fit over the chosen carburetor. Stock air filters have normally been provided without any particular emphasis on a design configuration that would tend to minimize pressure drop of the air stream as it flows through the device, or that would tend to provide a uniform flow downward air flow into the carburetor. Such prior art air filters have generally been of the type in which air is drawn radially inwardly through a vertical wall of a normally cylindrical air filter. In such devices, the air stream churns turbulently about in proximity of the center of the filter before being drawn downwards into the carburetor beneath the filter.
I am aware of various attempts, primarily in racing and other high performance applications, in which an effort has been made to improve the efficiency of the air flow design in air filters. Such attempts are largely characterized by design enhancements which make some sort of an attempt to smoothly guide the incoming air downwards into the carburetor. One such design is shown in U.S. Pat. No. 3,224,174 issued Dec. 21, 1965 to Erbstoesser for AIR-FEED DEVICE FOR CARBURETORS. In one embodiment, his invention provides a downwardly-pointed cone of solid metal or other suitable material to gather air and direct it toward a central opening therebelow. However, his device does not provide for a high efficiency air filtration device to be used in conjunction therewith. A somewhat similar design is disclosed in U.S. Pat. No. 3,347,028 issued Oct. 17, 1967 to Erbstoesser for AIR-FEED DEVICES FOR CARBURETORS. That design shows a combination air filter lid and flow smoothing cone shaped central interior wall. The design is not suitable to the retrofit of existing high performance air filters. Another design is illustrated in U.S. Pat. No. 3,670,480, issued Jun. 20, 1972 to Peterson for CLEANER. That device shows a cone-shaped center portion with a generally concave face and downwardly projecting drag ridges or ribs which cooperate with an annular rotating disc to separate particulates from the entering air stream. Like Erbstroesser, the Peterson design also lacks provisions for incorporation of a high efficiency filter.
For the most part, the documents identified in the preceding paragraph disclose devices which have one or more of the following shortcomings: (a) they do not include any means for retrofitting existing high efficiency air filters, and (b) some designs do not include provisions for high efficiency air filtration. Thus, the advantages of my simple insert design which may be retrofitted to existing high efficiency air filters are important and self-evident.